The invention relates to the field of analytical clinical chemistry and environmental residue monitoring and the detection and quantification of the antidepressant drug venlafaxine (IUPAC name: (RS)-1-[2-dimethylamino-1-(4-methoxyphenyl)ethyl]cyclohexanol). Introduced in the early 1990s, it belongs to drugs of the serotonin noradrenergic reuptake inhibitor class and is metabolized by the cytochrome P enzyme CYP2D6 to its major (and active) metabolite O-desmethylvenlafaxine (IUPAC name: (RS)-1-[2-dimethylamino-1-(4-hydroxyphenyl)ethyl]-cyclohexanol). There are clinical requirements for the detection, following drug overdose and for therapeutic drug monitoring, of both the parent drug and its main metabolite. There is also a need for their non-clinical detection, with venlafaxine being amongst the increasing number of pharmaceuticals detected in the environment (Daughton and Brooks 2010).
Current analytical methods use mass-spectrometry (MS) in conjunction with gas chromatography (GC) or liquid chromatography (LC). These methods are resource intensive, requiring expensive equipment and highly trained staff for their operation. Furthermore, use of these methods for the confirmation of venlafaxine use can be subject to uncertainty. Tramadol and O-desmethyl-venlafaxine were shown to have similar retention indices and overlapping fragmentation ions, leading to difficulties and uncertainty with the identification of tramadol in the presence of venlafaxine using a LC-MS-MS system (Allen 2006). In light of the current state of the art, what is required is a simplistic and economical detection method that is able to specifically detect venlafaxine and O-desmethylvenlafaxine.